Fuel-injection arrangement controlled in dependence upon the air inflow rate

ABSTRACT

A fuel-injection system for an internal-combustion engine having at least one engine cylinder, an air-intake passage communicating with the interior of such cylinder, a piston movable in such cylinder, and an engine crankshaft connected to such piston. The system includes an electrically actuatable fuel-injection valve having an electrical input for receipt of a valve-opening pulse and is operative for injecting fuel into the cylinder for a time interval corresponding to the duration of such valve-opening pulse. A triggering unit generates crankshaft-positionsynchronized triggering pulses. An airflow sensing unit determines the rate of airflow through the air-intake passage. A first pulse-generating unit is connected to the triggering unit and to the airflow sensing unit and is operative upon generation of a triggering pulse for generating a control pulse having a pulse duration dependent upon the airflow rate detected by the airflow sensing unit. A second pulse-generating unit is connected to the triggering unit and to the first pulse-generating means and is operative upon generation of a triggering pulse for generating a second control pulse having a pulse duration dependent upon at least one other variable engine operating condition. A composite valve-opening pulse comprised of said first and second control pulses is applied to the electrical input of the fuel-injection valve.

United States Patent Werner et al.

[ Aug. 12, 1975 FUEL-INJECTION ARRANGEMENT Primary EmminerCharles J. Myhre CONTROLLED lN DEPENDENCE UPON Aizrixlam bIwminer-Joseph Cangelosi THE MR [NFLOW RATE .il/Urlltj', Age/H" 0r Firm-Michael S. Striker [75] Inventors: Peter Werner, Schwieherdingen;

Ulrich Drews, Stuttgart; Norbert ABSTRACT Rmmannsbergerschwiebffrdingcn; A fuel-injection system for an internal-combustion en- Olfgang Stuttgart? Helmm gine having at least one engine cylinder, an air-intake Moder; both of passage communicating with the interior of such cylin- Schwleherdmgtsnof Germ'lmy dcr, a piston movable in such cylinder, and an engine [73] Assigneei Robert Bosch G.m.b.H., Stuttgart crankshaft connected to such piston. The system in- Germum, cludes an electrically actuatable fuel-injection valve having an electrical input for receipt of a valvel Filed: p 1973 opening pulse and is operative for injecting fuel into [21] APPL NOV: 3923" the cylinder for a time interval corresponding to the duration of such valve-opening pulse. A triggering unit generates crankshaft-position-synchronized triggering Foreign Appllcatlo" Prmr'ty Data pulses. An airflow sensing unit determines the rate of Aug, 3L 1972 Germany 2242795 airflow through the airintake passage. A first pulsegenerating unit is connected to the triggering unit and [52] US. Cl. l23/32 EA to the airflow sensing unit and is operative upon gen- [Sll lnt. Cl. 1 1 1 1 FOZM 5l/02 eration of a triggering pulse for generating a control [58] Field of Search 1, [23/32 EA pulse having a pulse duration dependent upon the airflow rate detected by the airflow sensing unit. A see- [56] References Cited ond pulse-generating unit is connected to the trigger- UN| D STATES PATENTS ing unit and to the first pulse-generating means and is 3,005.44? 10/196] Baumann et U1. 123/32 EA Operative genemfio" of triggering pulse for 3.612.008 10/1971 Beishir .1 123/32 EA generating Second Comm hwmg PuSC 31,369 1/1973 Sudu e u| 133/33 EA tion dependent upon at least one other variable engine 3.665.900 5/1972 Schlimme .1 123/32 EA p r ing ndi ion. A composite al -opening pulse 3.691003 9/1972 Wakamatsu et ul l23/32 EA comprised of said first and second control pulses is ap- .7()5.572 12/!972 Bloomfield 1, 123/32 EA plied to the electrical input of the fuel-injection valve, 3 8|7.226 6/1974 Wakamatsu et al. l23/32 EA 53 Claims, ll Drawing Figures ,5 O

I k-" 12 1s 2 2 l4 To J0 I V 3] *1 b PATENTED AUG 1 21975 SHEET z w ul m 4| 1 L mu. w u L1 105+ MLUPE PATENTED AUG 1 2 I975 SHEET Fig.9

Fig. 11

FUEL-INJECTION ARRANGEMENT CONTROLLED IN DEPENDENCE UPON THE AIR INFLOW RATE BACKGROUND OF THE INVENTION The invention relates to electrically operated fuelinjection arrangements for internal combustion engines provided with electrical ignition systems, in particular battery ignition systems.

More particularly, the invention relates to electri cally operated fuel-injection valves, each such valve being associated with a respective one of the engine cylinders and being periodically energized, to effect valve-opening, for varying time intervals, in order to vary the amount of fuel injected through the valve into the respective engine cylinder. Still more particularly. the invention relates to electrically operated fuelinjection arrangements of the type provided with means for generating electrical valve-opening pulses of varying duration applied to the electrically actuated fuel-injection valves for effecting valve opening for different periods of time, with the duration of the valveopening pulses being made to vary in dependence upon one or more engine operating conditions.

It is known to provide, for example, a four-cylinder engine with a fuel-injection arrangement comprised of four electrically actuated fuel-injection valves, one associated with each cylinder. A problem with such arrangements is that the electronic control circuitry necessary to properly control the operation of the fuelinjection valves must be designed in different ways, depending upon whether the fuel injection valves to be operated will be operated in unison, in groups of two (in the case of engines having an even number of cylinders) or in groups of four (in the case of four-cylinder, eight-cylinder and twelve-cylinder engines).

SUMMARY OF THE INVENTION It is the general object of the present invention to provide a fuel-injection arrangement which is more advantageous than the arrangements of the prior art.

It is another object of the present invention to provide a fuel-injection arrangement which is more versatile than the systems known in the prior art.

It is still a more particular object to provide a fuelinjection arrangement comprised of electronic control circuitry particularly designed for realization in integrated-circuit form.

It is a still more specific object of the invention to provide an electronic control circuit for such a fuelinjection system in intcgrated-circuit form and comprised of integrated-circuit functional groups which are combinable in a highly versatile manner, so as to facilitate the adaptation of a particular system to the requirements of a particular engine.

These objects. and others which will become more understandable from the following description can be met, according to one advantageous concept of the present invention by providing, in a fuel-injection system for an internal-combustion engine having at least one engine cylinder, an air-intake passage communieating with the interior of such cylinder, a piston movable in such cylinder, and an engine crankshaft connected to such piston. in combination, an electrically actuatable fuel-injection valve having an electrical input for receipt of a alve-opening pulse and operative for injecting fuel into said cylinder for a time Interval corresponding to the duration of such valve-opening pulse; triggering means for generating crankshaft-position-synchronized triggering pulses; airflow sensing means for determining the rate of airflow through said air-intake passage; first pulse-generating means connected to said triggering means and to said airflow sensing means and operative upon generation of a triggering pulse for generating a control pulse having a pulse duration dependent upon the airflow rate detected by said airflow sensing means; second pulse-generating means connected to said triggering means and to said first pulse-generating means and operative upon generation ofa triggering pulse for generating a second control pulse having a pulse duration dependent upon at least one other variable engine operating condition; and means for applying to said electrical input of said fuel-injection valve a composite valve-opening pulse comprised of said first and second control pulses.

The novel features which are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, to gether with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a functional block diagram of one fuelinjection system according to the invention;

FIG. 2 is a detailed circuit diagram of certain of the functional blocks in the diagram of FIG. I;

FIG. 3 is a graphical depiction of certain aspects of the operation ofthe circuit components shown in FIGS. 1 and 2;

FIG. 4 is a detailed circuit diagram of the charging circuit A shown in FIG. 2;

FIG. 5 is a detailed circuit diagram of the discharging circuit E shown in FIG. 2;

FIG. 6 is a detailed circuit diagram of a charging circuit of the type shown in FIG. 4, but provided with a speed-compensation feature;

FIG. 7 is a modified version of the circuit shown in FIG. 4, but provided with a speed-compensation feature;

FIG. 8 is another modified version of the circuit shown in FIG. 4, provided with a speed-compensation feature;

FIG. 9 is a graphical depiction of certain aspects of the operation of the circuit shown in FIG. 6;

FIG. I0 is a detailed circuit diagram of one of the functional blocks shown in FIG. I; and

FIG. I I is a detailed circuit diagram of another of the functional blocks shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The illustrated fuel-injection arrangement is adapted for a battery-ignition four-cylinder four-stroke internal combustion engine I, and comprises four electromagnetically actuated fuel-injection valves 2 which receive fuel to be injected via respective fuel conduits 4 from a distributor 3. The arrangement further includes an electromotor driven fuel pump 5. a pressure regulator 6 which maintains the fuel pressure substantially constant. and also an electronic control system triggered by the engine ignition system once per crankshaft rotation in a manner described in detail below. When triggered. the control system generates an electrical rcct angular valveopening pulse .l\ for the fuel-iniection valves 2. The duration Tv of these alveopcning pulses Jv determines the duration of the time interval for which the fuel-in ection \ahes Z are opened. and accordingly determines the quantity of fuel which will be injected by the val\e during its open time interval.

The magnetic windings 7 of the fuel-in ection valve 2 are each connected in series with a decoupling resistor 8 and jointly connected to the output current path of a power amplifier stage 10 which contains at least one power amplifier transistor ll having an emitter collector path connected to carry energizing current for the magnetic windings 7 and having an emitter con nected to the grounded negative terminal of a nonillustrated battery.

Gasoline engines provided with discrete ignition systems of the type in question use per combustion cycle only as much fuel as can be completely burned when combusted with the amount of air sucked into the engine cylinder during the respective piston air-intake stroke. On the other hand. for efficient operation of the engine it is necessary that no substantial excess of air remain in the combusted fuel-air mixture at the end of the working stroke. To measure the inflow rate of air into the air intake passage 12 of the engine, an airflow sensing member in the form of a pivotable baffle plate I5 is located in the air intake passage 12 upstream of the throttle valve 14 controlled by the gas pedal l3. Pivot-able baffle plate 15 is biased by a non-illustrated return spring in a direction opposing the force of inflowing air, and assumes in the steady state a deflected position indicative of the average air inflow rate Sharing the pivoting movement of baffle plate 15 is the wiper l6 of a potentiometer 17. The voltage at the potentiometer wiper is indicative of the position of the baffle plate 15 and thereby indicative of the air inflow rate. This voltage is used as a control voltage for the control arrangement described below.

The control arrangement includes means for the generation of triggering signals. a pulse-shaping stage 21, a frequency-divider stage 22, and a control multivibrator 23 connected to and cooperating with means 24 for prolonging the duration of the pulses generated by multivibrator 23. The functional cooperation of units 23 and 24 is explained in detail below. A voltage compensating stage 25 is connected to the output of means 24 and serves the purpose of counteracting the undesirable effect which battery voltage variations tend to have upon the duration Tr of the valve-opening pulses Jr. The control multivibrator 23 furnishes at its output control pulses J0 having a pulse duration To dependent upon the setting of potentiometer l7 and thereby dependent upon the detected air inflow rate. These control pulses Jo are applied to the pulseprolonging unit 24 which increases the duration of each such pulse Jo by a predetermined factor f which varies in dependence upon the position of the throttle valve, as indicated by an engine-load indicating unit 26, and also in depen dence upon the existence of certain other specific engine conditions. such as whether the engine is being started, as indicated by a starting indicator 26, so that the fuel-air mixture being combusted can be enriched under such circumstances, or whether the engine is being run up. The voltage pulse generated at the output of pulse-prolonging unit 24 has. as lust nientloned a duration equal to the duration lo of the pulse Jo plus the duration lo n'iultiplied n a factor f dependent upon the aboic-mentioncd variables. and upon any other operating conditions to be taken into account. l'he thusly prolonged pulse appearing at the output of unit 24 is applied to the input of hattcry-\oltagecompensating means 25 which prolongs the pulse fur nished by unit 24 to an extent dependent upon the pre' \ailing battery voltage, this prolongation increasing as the battery voltage decreases. for example as a result of long use of the battery. This further battery-voltagedependent prolongation of the valve-opening pulse is necessary to take into account the finite pull-in and drop times of the electromagnetically actuated fuelinjection valves and the dependence of such pull-in and drop times upon the voltage applied to such valves.

As will become clearer subsequently, the leading edge of the actual valve-opening pulse Jr is generated substantially simultaneously with the generation of the leading edge of the control pulse Jo, this moment being essentially determined by the moment that the engine crankshaft assumes a predetermined angular position. In this embodiment the generation of pulses Jo and Jr is triggered by the erankshaftposition-synchronized triggering pulses which are generated by triggering stage 20 of the non-illustrated ignition arrangement of the engine. These crankshaft-position-synehronized triggering pulses are generated in response to opening of the interruptor switch by the action of a crankshaft-operated cam 31. The actual triggering pulse produced by stage 20 is taken off the upper stationary terminal of switch 30, as is particularly evident from FIG. 2, leftmost portion. In FIG. 2 it is shown that the interruptor switch 30 is connected in series with the primary winding 33 of the ignition transformer of the engine ignition circuitry.

The detailed circuit diagram shown in FIG. 2 is particularly suited to the integrated-circuit manufacture approach. The illustrated pulse-shaping stage 21 is provided at its input with a safety stage for the suppression of false triggering signals such as can result from sud den changes in the energy delivery from the power supply, i.e.. such as can result from sudden changes in the energy delivery occurring over positive supply line 35 and negative supply line 36. Such sudden changes in the supplied voltage and/or current result most often from the turning on or off of some electrically operated vehicle component or accessory. This safety stage is comprised of a pnp transistor 37 having a base connected to positive line 35 and an emitter connected to the tap of a voltage divider formed by two fixed-value resistors 38 and 39, connected in parallel across the circuit branch containing the interruptor switch 30, 32. Connected in parallel to voltage-divider resistor 39 is a capacitor 40. as well as a diode 41 having its anode connected to the negative line 36. Transistor 37 can become conductive only if the potential at its emitter becomes sufficicntly higher than the potential at its base. this base potential being equal to the potential of the positive supply line 35. This happens when interruptor switch 30, 32 opens. Such opening of interruptor switch 30, 32 produces a sudden decrease in the current flowing through primary 33 of the ignition transformer. This sudden decrease of current flow results in the generation across primary 33 ofa high-voltage voltage spike having a magnitude many times the magnitude of the voltage across the supply lines 35, 36. The relative resistance values of voltage-divider resistors 38. 39 are so selected that only a voltage of this extremely high magnitude is capable of rendering transistor 37 conductive. In this manner, the safety stage permits conduction by transistor 37 only in response to triggering pulses actually generated by the crankshaftactuated interruptor switch 30, 32, only these trigger ing pulses being of the high amplitude in question. lnasmuch as the voltage spike resulting upon opening of interruptor switch 30, 32 will be very short-lasting, the conduction time of transistor 37 will he correspondingly short-lasting.

Connected to the collector of transistor 37, via a resistor 42, is the base of an npn transistor 43 which, together with a second npn transistor 44, forms a monostablc multivibrator. this monostable multivibrator furthermore including transistor 45 and coupling capacitor 46. The base of transistor 45 is connected to the collector of transistor 43, and is furthermore connected to the negative line 36, via two resistors 47 and 48. The junction between resistors 47 and 48 is connected to one of the two electrodes of coupling capacitor 46, and is furthermore connected to the emitter of transistor 45. Transistor 45 serves for the quick recharging of the coupling capacitor 46 of the multivibrator, when the multivibrator reverts to its stable state; this quick re charging of multivibrator capacitor 46 is important because, if capacitor 46 is not charged up to its full voltage by the time of receipt of the next triggering pulse, the duration of the unstable state produced by such next triggering pulse will be shorter than if the capacitor 46 had had time to fully charge. The quick recharging of multivibrator capacitor 46 assures that the duration of the unstable state of the monostable multivibrator will be dependahly constant.

The circuit furthermore includes a transistor 51 acting like a Zener diode by virtue of the short-circuiting of its base-collector path. The emitter of transistor 51 is connected to the base of an npn emitter-follower transistor 52, and is furthermore connected to the positive line via a biasing resistor 53. The transistors 51 and 52 cooperate to assure that capacitor 46 will always charge up to the same value, when the monostable multivibrator reverts to its stable state, irrespective of variations in the voltage supplied by the vehicle battery, and cooperate to assure that the duration of the unstable state of the multivibrator will always be the same despite such variations.

Resistor 48 serves to maintain transistor 45 conductive after the charging of capacitor 46 via the collectoremitter path of transistor 45 is completed. In this way, the emitter of transistor 45 is maintained at a definite predetermined voltage, which it assumes at the end of the rapid charging of capacitor 46. By such measures, the duration of the unstable state of the monostable multivibrator formed by transistors 43 and 44 is maintained substantially independent of engine speed, i.e., independent of the pulse repetition frequency of the triggering pulses generated by interruptor switch 30,

If the resistor 48 were not provided, capacitor 46 could still become quickly charged via conductive transister 45. However, as the voltage across capacitor 46 would increase, the emitter voltage of charging transistor 45 would rise. thereby reducing the base-emitter voltage of transistor 45, and making transistor 45 less and less conductive, until finally it would become altogether nonconductive. After transistor 45 would be come nonconductive. the capacitor 46 would continue to charge. although at a much slower rate. through base-emitter biasing resistor 47 and through the collector resistor 49 of transistor 43. As a result of this continued but very slow charging, the total amount of charge accumulated on capacitor 46 at the time of re ceipt of the next triggering pulse would be a function of the time interval between triggering pulses. and accordingly a function of engine speed, which is undesirable. This difficulty could not be overcome by further omitting the base-emitter biasing resistor 47, because then the diode-like character of the base-emitter junction of transistor 45, which permits charging of capacitor 46, would prevent the necessary subsequent discharging thereof.

When the monostable multivibrator of stage 21 is in its stable state, transistor 44 is maintained in its conductive state by an adjustable resistor 54 connected to the emitter of transistor 52. However, in the stable state of the multivibrator, transistor 43 is non-conductive by virtue of the connection thereto of coupling resistor 55. Likewise. the output transistor 56 of pulse-shaping stage 21 is also nonconductive. when the multivibrator is in its stable state, because of the voltage applied to the base of transistor 56 from the tap of the voltage divider formed of resistors 55, 57 and 58.

The frequency-divider stage 22 connected to the output of pulse-shaping stage 21 is comprised of a bistable multivibrator which includes two npn transistors 61 and 62. The emitters of transistors 61 and 62 are connected to the negative line 36, and the collectors of these transistors are connected to the positive line 35 via respective collector resistors 63 and 64. The bases and collectors of transistors 61, 62 are cross-coupled by means of coupling resistors 65, 66 in the conventional bistable multivibrator configuration. The bases of transistors 61, 62 are connected to ground via respective grounding resistors 67 and 68. The bases of transistors 61, 62 are each connected to the anode of a respective one of diodes 69, 70, the cathodes of which are connected via respective coupling capacitors 71, 72 to the collector of output transistor 56 of pulseshaping stage 21.

The two output voltages of the illustrated bistable multivibrator are the voltages across the two collector resistors 63 and 64. In conventional bistable multivibrator fashion. one of these voltage drops will be large when the other is small, and vice versa, due to the fact that when a respective one of the multivibrator transistors 61, 62 is conductive the other one of transistors 6t, 62 will be non-conductive. To couple these two output voltages out of the bistable multivibrator circuit, and to ensure that there will be no reaction back upon the bistable multivibrator output components from circuit stages connected to the output of the multivibrator, two emitter-follower transistors 73 and 74 are provided. The base-collector paths of these emitterfollower transistors 73, 74 are connected across respective ones of the two collector resistors 63, 64. Connected across the base-emitterjunctions of the emitterfollower transistors 73, 74 are diodes 75, 76, connected with a polarity opposite to the polarity of the pn baseemitter junction of the respective emitter-follower transistor.

The junction between the emitter of transistor 73 and the anode of diode 75 is connected. via a resistor 77, to the junction between the cathode of diode 69 and coupling capacitor 7]. Likewise. the junction between the emitter of transistor 74 and the anode of diode 76 is connected. via a resistor 78, to the junction between the cathode of diode 70 and the coupling capacitor 72. Also connected to the emitter of emitter-follower output transistor 74 is a circuit branch comprised of the series connection of a resistor 79 and a diode 82. The circuit branch 79, 82 conducts the output voltage of the bistable multivibrator. that is. conducts the emitter voltage of output transistor 74, to the input of the control multivibrator 23, as described in greater detail below.

In conventional bistable multivibrator fashion, the multivibrator transistor 61 is non-conductive when the multivibrator transistor 62 is conductive, and vice versa. Each time that a triggering signal is generated upon brief opening of the interruptor switch 30, 32, the output transistor 56 of pulse-shaping monostable multivibrator stage 2] becomes briefly conductive, to transmit a rectangular triggering pulse, as described earlier. This effects a change of state of the bistable multivibrator stage 22. That is. the conductive one of multivibrator transistors 61, 62 becomes non-conductive, and vice versa. In this manner, a first triggering pulse will for example render transistor 6l conductive, while the next triggering pulse will render transistor 62 conductive. with the subsequent triggering pulse rendering transistor 61 conductive again. and so forth. It is for this reason that the voltage drop across collector resistor 63 will be great when the voltage drop across collector resistor 64 will be small, and vice versa.

The relationship between the output pulse generated by the bistable multivibrator stage 22 and the successive ignition operations performed by the nonillustrated ignition circuitry, is depicted in FIG. 3. The engine is provided with four cylinders Z1, Z2, Z3 and Z4, the order of operation of these cylinders being ZI, Z4. Z3, 22. In FIG. 3 the diagonally hatched rectangular areas indicate the duration of the air-intake stroke of each cylinder, measured in degrees of crankshaft rotation.

FIG. 3 also depicts the train of output pulses 80 of the bistable multivibrator 22. It will be evident that the frequency of this train of output pulses 80 is equal to one half the frequency of the ignition timing pulses generated upon brief opening of the crankshaft-synchronized interruptor switch 30, 32. In FIG. 3 the moments of generation of these ignition timing pulses are indicated by the lightning-bolt symbols.

As mentioned earlier. with regard to FIG. I. the out put voltage pulses from frequency-halving bistable multivibrator 22 are applied to the input of a control monostable multivibrator 23 which generates at its output a control pulse Jo having a duration To dependent upon the rate of air inflow into the engine air-intake passage 12.

There are two different ways in which a monostable multivibrator such as control multivibrator 23 can be made to generate variable-duration control pulses Jo having a duration dependent upon the air inflow rate. In general. the timing capacitor C (FIG. 2) of the monostable multivibrator will be charged by a constant-current source of charging current. for a time interval corresponding to a fixed angle of crankshaft rotation. and then discharged through a constant-current discharging circuit. for whatever time interval is necessary to discharge the timing capacitor at the selected discharge rate. The duration To of the control pulse .10 5 will be equal to the duration of the discharge time of the capacitor C. as can be seen in FIG. 3.

Now. there are two different ways of making the duration of the discharge time for the timing capacitor C dependent upon the air inflow rate. As a first possibility. the timing capacitor C can be charged with a constant current whose magnitude is automatically adjusted in proportion to the air inflow rate, and then discharged with a constant discharge current having a preselected value independent of the air inflow rate. With this approach, the charge built up on the capacitor at the commencement of discharging will be dependent upon the air inflow rate. and accordingly the discharge time for the timing capacitor will also be dependent upon the air inflow rate. The value of the charging current. with this approach, will be determined by the voltage furnished by potentiometer 17 (FIG. 1 to the control input of control monostable multivibrator 23.

As a second possibility, the timing capacitor C can be charged with a constant charging current having a fixed preselected value independent of the air inflow rate, and then discharged with a discharge current having a value inversely proportional to the detected average air inflow rate. In the illustrated embodiment. this second approach is adopted. This approach offers the advantage that any changes in the average air inflow rate occurring during actual generation of the control pulse J0. i.c.. any changes in the air inflow rate occurring during the time interval To. will cause an appropriate shortening or lengthening of the pulse duration To. and accordingly a somewhat higher accuracy may be achieved than with the first possibility mentioned.

The circuit details of the control monostable multivibrator 23 are depicted in FIG. 2. The multivibrator 23, besides the requisite timing capacitor C. furthermore includes two pnp multivibrator transistors T] and T2. The emitters of transistors T1 and T2 are directly connected to the positive line 35. Connected to transistors T] and T2 in Lin-configuration are respective additional transistors TH and Tl2. The base of multivibrator transistor T1 is connected, via a resistor 85. to the positive line 35, and when monostable multivibrator 23 is in its stable state. multivibrator transistor TI is nonconductive. The base of transistor T1 is additionally connected. via a circuit branch 84 including a coupling capacitor 87. to one of the two outputs of bistable multivibrator 22, specifically the emitter of emitterfollower output transistor 73 of bistable multivibrator 22. Finally. the base of multivibrator transistor TI is furthermore connected, via a resistor 88, to the collector of a transistor 74. The emitter of transistor T4 is connected directly to the negative line 36, while its base is connected to the tap of a biasing voltage divider formed of resistors 90 and 91. Resistor 90 is connected to the negative line 36, whereas resistor 91 is connected to the collector of a biasing transistor T3, and is furthermore connected via a resistor 92 to the positive line 35. The base of biasing transistor T3 is connected to the junction between two resistors 93. 94 which are connected in the collector circuit of the Lin circuit T2, T12. The base of transistor T3 is furthermore connected via a resistor 95 and conductor 84 to one of the two outputs of the bistable multivibrator 22.

The collector of transistor T3 is connected, via a resistor 96, to the base of a transistor T5. with the junction between resistor 96 and the base of transistor T being connected to the negative line 36 via a resistor 97. Connected to the collector of transistor T5 is the base of an output transistor T6. It will be evident to persons skilled in the art that changes in the collector voltage of transistor T5 produce inverse changes in the collector voltage of output transistor T6. The output control pulses .Io are tapped off the collector of output transistor T6.

The control monostable multivibrator 23 operates in the following manner:

First, the multivibrator timing capacitor C is charged by a constant charging current Ia for a time interval corresponding to a fixed predetermined angle of crankshaft rotation. The voltage across the timing capacitor C rises linearly, as depicted graphically in FIG. 3. In the illustrated embodiment. the duration of the charging time interval for timing capacitor C is equal to the time interval required for the crankshaft KW to turn through 180. In the graphical representation of FIG. 3, the charging of the capacitor C occurs as the crankshaft KW moves from the 540 position to the 0 position; the 0 position of crankshaft KW is the same as the 720 position, the crankshaft rotational cycle being considered as consisting of two complete rotations, i.e., an angular rotation of 720 per crankshaft rotational cycle. Charging of timing capacitor C also occurs as the crankshaft KW moves from its [80 position to its 360 position, and as the crankshaft moves again from its 540 position to its 720 position (0 position).

During the charging intervals for timing capacitor C, the voltage output 80 at the emitter of output transistor 73 of bistable multivibrator 22 is at its upper level. Accordingly, during these charging intervals, the voltage output 81 at the emitter ofoutput transistor 74 of bistable multivibrator 23 will be at its lower level, this voltage 81 controlling the operation of charging current source A.

The charging current la flowing into timing capacitor C during the charging interval between times tI and 12 (FIG. 3) produces a linear rise of the voltage Uc across the capacitor C. The peak value of the capacitor voltage Uc is reached at the 360 and 720 (0) positions of the crankshaft KW, and is inversely proportional to the prevailing engine speed. During this charging interval, transistors T1 and T1] are non-conductive, whereas transistors T2 and Tl2 are conductive and thereby maintain transistor T3 conductive and therefore transistor T4 nonconductive. In a redundant manner. transistor T3 is furthermore maintained conductive by the high value of voltage 80 applied via resistor 95 to the base of transistor T3. Accordingly, if the voltage across power supply lines 35, 36 should for any reason momentarily decrease in a manner tending to lower the base-biasing voltage at the junction between resistors 94 and 93, sufficient base-biasing voltage will nevertheless be applied from output 84 of bistable multivibrator 22, via resistor 95, and accordingly premature termination of the charging operation will be prevented.

The charging operation will terminate only at time [2. at which crankshaft KW assumes its 360 or 720 posi- LII . 6 tion, and at which output voltage Wlll drop to its base level. In response to this sudden drop in the voltage level of output signal 80, differentiating capacitor 87 will transmit a negative triggering pulse to the base of multivibrator transistor TI, via resistor 86, rendering transistor T1 conductive. Simultaneously therewith, the voltage level of the other multivibrator output signal 81 undergoes a sudden rise from its base level to its upper level, thereby terminating operation of charging current source A. By virtue of the charge on timing capacitor C, the voltage Uc thereacross will now be of such a polarity and have such a magnitude as to render previously conductive transistors T2 and T12 nonconductive. As a result. transistor T3 becomes nonconductive. and transistor T4 becomes conductive.

Charged timing capacitor C now begins to discharge through constant-current discharge device E, and the capacitor voltage Uc decreases linearly. When the capacitor voltage Uc decreases to a value near zero, the capacitor voltage no longer can maintain transistor T2 non-conductive. As a result. transistor T2 becomes conductive. Despite the fact that output signal 80 is still at its base value, and therefore incapable of rendering transistor T3 conductive via resistor 95. transistor T3 nevertheless does become conductive when transistor T2 becomes conductive. This is because the collector current of transistor T2 flows to ground through voltagedivider biasing resistors 91, 90, and the voltage developed at the junction of these two resistors renders transistor T3 conductive. As a result. transistor T4 becomes non-conductive. The decrease of the capacitor voltage Uc to this near-zero value, causing the justmentioned turn-on of transistors T2 and T3 and the just-mentioned turn-off of transistor T4. occurs at time t3, as shown in the graphical representation of FIG. 3.

It will be evident that when the discharge of capacitor C began, at time 2, the turn-off of transistor T3 caused a turn-on of transistor T5, and a consquent turn-on of output transistor T6. When output transistor T6 hecame non-conductive in this manner (at time [2) its collector voltage rose suddenly, producing the leading edge of the control pulse J0. Conversely. at the end of the capacitor discharge. at time t3, the turn-on of transistor T3 renders transistor T5 non-conductive and therefore transistor T6 conductive. The collector voltage of T6 accordingly falls. and the control pulse Jo ends.

FIG. 4 depicts circuit details of a constant current source, which in principle can be employed either as the charging source A or as the discharging device E of FIG. 3.

The constant current source of FIG. 4 is comprised of an operational amplifier Pl whose positive noninverting input. via a compensation circuit comprised of transistor T10, resistors 102, I08, 101 and 103. is connected to the emitter of the Darlington-circuit transistor T9. With the provision of transistor T10, the charge on the capacitor 107 need change only very little when the circuit is switched on or off. During the time the charging circuit of FIG. 4 is switched on. the output voltage 8] is at its base or zero value and accordingly the control current Is indicated in FIG. 4 is zero; furthermore. the base and emitter of transistor T10 will be at approximately the same voltage. As a result, transistor 10 is non-conductive and initially inoperative. The connection point N of capacitor I07 is maintained at a fixed predetermined potential determined by the internal circuitry of the operational amplifier Pl. At the same time, the potential at the connection point M (emitter of T9) of the second capacitor electrode is determined by the voltage across \olt agcalhidcr resistor 11)}. It is in this manner that the \oltagc across capacitor 107 is established At time t2. crankshaft KW is in its .160 or 71H" position. and the second output \oltage 81 jumps to its upper le\el. thcreliy ending the charging operation by terminating operation of the charging current source A. At circuit junction N the final value of the current Is is stored in the operational amplifier P1. but the potential at circuit junction does not changev The output 8 of the operational amplifier assumes a potential so slight as to render non-conductiye both Darlingtoncircuit transistors T8 and T9. and the flow of charging current la is accordingly terminated. If transistor T10 were not present. the potential at circuit junction M would at this time become zero. which would produce a marked change of the charge on capacitor 107. Such change of the charge on capacitor 107 would result in the ahovementioned delay when the flow of charging current la is subsequently re-estahlished. for the next cy clc of operation. The cmitter follower transistor T11), now. instead of the Darlington transistors T8 and T9. scr\ es to keep the potential at point M approximately at the value established by the voltagedivider resistors 108 and 103, so that the charge on capacitor 107 can change only slightly. When the constantcurrent charg ing source of FIG. -I is subsequently turned on again. for the next cycle of operation, the voltage increase at point M. in so far as resistor 108 is almost Zero. need amount to no more than the magnitude of the base emitter threshold voltage of transistor T10, until the charging current reaches its full value. In this way. initiation of the operation of charging current source A occurs \ery rapidly. Resistor I08 serves to reduce still fur ther the delay created by the provision of capacitor 107.

HO 5 depicts a discharge circuit. corresponding to the discharge de\ice E of FIG, 2. adapted to discharge timing capacitor C of FIG. 2. with a discharge current Ie hai ing a value imcrsely proportional to the detected average air intlow rate. The circuit shown in HQ. 5 is particularly suited for integrated-circuit production techniques.

The discharge circuit of FIG. 5 is comprised of a first operational amplifier P2 and a second operational arn plitier P3. the first operational amplifier P2 being similar to the operational amplifier P1 of FIG. 4. but having no input for the receipt of synchronized control signals. The positive input of operational amplifier P2 is connected. via a current limiting resistor 121. to the jund tion between two voltage-divider resistors 122 and 123. The output B of operational amplifier P2 is connected to the base of a transistor 1 18. which is connected in Darlingtonconfiguration with a further transistor T18. 'l he Darlington combination carries the discharge current le for the capacitor C of FIG. 2.

At circuit point M an electrode of an integrating capacitor 127 in the feedback network is connected to the emitter or transistor ll). A resistor 124 is con nected between the output of operational amplifier P2 and the positive line 35. The negative input of the operational amplifier P2 is connected to the circuit junction M.

The second operational amplifier P3 has its positive input connected to the adjustable wiper 16 of the potentiometer 17 shown in FIG. I. the potentiometer I7 being connected in series with resistors 12b and 129 across the supply lines 35 and 36.

llic junction H bet ecn resistor I26 and potentioin ctcr 17 is connected. via resistor 128. to the voltagedi\ider tap of \oltage divider 122. 123. This voltage divider tap is connected. \ia a compensation resistor 121. to the positi\e input of operational amplifier P2. A resistor 130 connects the circuit junction H to the positive input of second operational amplifier P3. The negative input ofoperational amplifier P3 is connected to the output thereof. Also connected to the output of operational amplifier P3 are an integrating capacitor 131 and a resistor 132 which connect the output of operational amplifier P3 to the circuit junction M and to the negative input of the first operational amplifier P2.

Resistors 121 and 128 serve for compensation and. ideally, exhibit no voltage drop. Accordingly the potential at the circuit junction H between resistors 128 and 130 is approximately the same voltage which is applied to the positive input of operational amplifier P2. The latter acts as a voltage follower and estahlishes the same potential at the circuit junction M. to which is also connected the resistor 132 which determines the magnitude of the discharge current le.

The second operational amplifier P3 also operates as a voltage follower or impedance converter. It transmits the voltage at the only slightly loaded potentiometer wiper 16 to that terminal of resistor 132 which is con nected to capacitor 131. so that the voltage on the latter is practically identical to the control voltage Us hetvveen the potentiometer wiper 16 and the circuit junction H As a result. the emitter current of the Darlington circuit is determined solely by the control voltage Us and the resistor 132. In the collector circuit of the Darlington transistors T18 and T19 there is made to How a discharging current le having a value inversely proportional to the measured air inflow rate.

The resistors 126 and 129, together with the potcntr ometer 17. can be built a unit forming part of the airflow-responsive baffle plate arrangement. separate from the electronic control circuitry to which it will subsequently be connected. With resistors 126 and 129 the voltage range within which voltages forjunctions H and M can he established can be so selected that. even with lowered battery voltages, the input range of the operational amplifiers P2 and P3 will not be exceeded. This is particularly important in view of the range of variation of the air inflow rate between idling and fullload engine conditions. the maximum such air inflow rate heing often as high as forty times the minimum air inflow rate. Selecting the potential at circuit junction H so high also prevents the peak value of the collectoremitter voltage of thc Darlington transistors T18. T19 from becoming too high. The capacitors 121 and 131 suppress effectively the tendency of both operational amplifiers to go into oscillations. The resistor 121, in cooperation with the other resistors. ser\ es to preclude the input currents of the first operational amplifier P2 from having an influence upon the discharge current le. Approximately. the resistance of resistor I21 corre sponds to the resistance of resistor 132 minus the resis tance of resistor I28 and minus the resistance of hias ing resistor 126. Resistors 122 and 123 make it possible to compensate for the offset voltage of the two opera tional amplifiers. inasmuch current flowing from voltage divider 122 123 into junction H via resistor 128 can have exactly such a value. that a voitage drop oil corresponding to the difference ofthe offset voltages of the operational amplifiers can be de\eloped across the series combination of the resistor 128. the effective re sistance of resistors I26 and 129, and the potentiometer 17. When this condition is met. and when furthermore the resistance of resistor 121 is properly selected. the discharge current le flowing in the emitter circuit of the Darlington transistor T19 will have a value corresponding to the quotient of the control \oltage Us and the resistance of resistor 132.

As depicted in FIG. I. the output of control monostable multivibrator 23 is connected to the input of a pulse-duration prolonging stage 24, to create the possi bility of varying the duration Tr of the valve-opening pulse .lv in dependence upon a plurality ofengine operating conditions. in a manner described in detail below. Experimentation has indicated that a fuel-injection arrangement which controls the quantity of injected fuel in dependence upon the air inflow rate, as measured by means such as the baffle-plate arrangement of FIG. 1. must select the quantity of fuel to be injected not only as a function of air inflow, but also as a function of engine speed. but only when the airflow rate reaches a certain value. corresponding to a certain angular deflection of the airflow sensing member 15, for example more than Advantageously. such a dependency of the duration of the valve-opening pulse upon engine speed should be established not in the pulse prolonging stage 24, but earlier. in the control monostable multivibrator 23, because speed-dependent variations of the duration of the pulse generated by monostable multivibrator 23 will be effectively multiplied by the prolonging action of pulse prolonging stage 24.

FIGS. 6 and 9 depict two embodiments of a speed compensation circuit according to the invention. Before discussing these circuits. it is thought advisable to explain in detail the functions they are intended to serve.

When the engine speed it exceeds approximately 2000 rpm, variations in engine speed should not have any effect upon the duration Tv of the valve-opening pulse Jr. In the speed range below 2000 rpm there should be a gradual reduction of the valve-opening pulse duration Tr with decreasing engine speed. Thus, if the engine speed goes down to 600 rpm the pulse duration Tv should be only about 80% of what it would be for the same air inflow rate but absent such enginespeed compensation.

This desired speed compensation is achieved by suitable control of the charging current Ia for the multivibrator timing capacitor C of FIG. 2. Specifically, the timing capacitor C is charged with a current Ia having a fixed predetermined value, but only for a time interval T; (see FIG. 9). After time interval Tz has elapsed, the charging current la is reduced to a lower predetermined fixed value which effects capacitor charging in a slower manner.

The graphical depiction of FIG. 9 makes clear the desired principle of operation. At the moment I] that the frequency divider 22 initiates the charging operation, a monostable multivibrator is triggered to its unstable state. and the multivibrator remains in this state for a time interval T1. During the time interval T2, the charging current has a predetermined fixed value In I, uncorrected for engine speed. and the timing capacitor voltage Uc rises in a proportionately linear manner. After the elapse of the delay interval Tz, the monostable mul tivibrator returns to its stable state. and effects a reduction in the magnitude of the charging current to a lower second value lul so that the capacitor voltage l t' con tinues to rise in a linear manner. but much more gradually.

In FIG. 9. the upper pulse train represents the output pulses of the bistable multivibrator 22. The interval between successive pulses is equal to Tp and corresponds to one half the reciprocal of the engine rotational speed. It will be evident from FIG. 9 that if the engine speed is such that the time interval Tp between successive output pulses of the bistable multivibrator 22 is less than T; then capacitor C will always charge up at the same rate. However, if the time period Tp is greater than T;. the charge which builds up on capacitor C varics as a function of engine speed and will. with decreasing engine speed. deviate more and more from the value which it would have had (indicated in dashed lines) if engine-speed compensation were not present.

FIG. 6 depicts circuit details of an exemplary embodiment of a timing-capacitor charging arrangement similar to that shown in FIG. 4 but provided with one of several possible means for varying the charging of the timing capacitor in dependence upon engine speed in the mannerjust explained with reference to FIG. 9. The circuit includes a switch coupled (via a nonillustrated linkage) with the engine throttle valve 1-1. Switch 140 remains in its illustrated closed position so long as the throttle valve is in its closed position. Switch 140 opens only if the gas pedal 13 is depressed to such an extent to cause the throttle valve to open and pivot through an angle in excess of 30. This extent of throttle valve opening actuates the engine-speed compensation means.

The circuit of FIG. 6 is comprised of an npn transistor T14 forming part of a triggerable monostable circuit. The emitter of transistor T14 is connected to the negative line 36. and its base is connected via diode 141, a resistor 144 and a capacitor 143 to the output 81 of the bistable multivibrator 22. Capacitor 143 is operative for controlling the operation of the illustrated circuitry only when switch 140 is open; otherwise, one terminal of the capacitor 143 is grounded. When switch 140 is open, the flip-flop output voltage 81, when in its upper level, can charge capacitor 143 through resistor 142, diode 141 and base-emitter biasing resistor 144. At time II, when the charging of multivibrator capacitor C begins, and when the flip-flop output voltage 8l reverts to its base value, the voltage which has built up across the capacitor I43 maintains transistor T14 nonconductive for such time as is required for capacitor 143 to discharge through resistors 145 and 142. The time which elapses until T l 4 again becomes conductive is Tz (FIG. 9). The collector of transistor T14 is connected, via collector resistor 146, to the positive line 35. So long as transistor T14 is kept non-conductive, it maintains transistor T15 conductive. So long transistor T14 is maintained non-conductive. whether by the action of charged capacitor 143 as just described, or by the action of grounding switch 140 when the latter is closed, transistor T15 will be conductive and carry current flowing through its collector resistor 147 and through its collector-emitter path, in parallel with the current path formed by charging resistor 105. The provision of this additional current path in parallel with the charging resistor 105 results in an increase in the charging current Ia to a higher value la]. If throttle-valvecontrolled switch 140 remains open, but the capacitor 140 has discharged, after elapse of a time interval T2 as described above, then transistor T14 becomes conductive again, as explained above, causing transistor T15 to become non-conductive. As a result, there is no longer an auxiliary conductive path connected in parallel with charging resistor 105. and the charging current la accordingly falls to a lower value laZ, so that further charging of multivibrator timing capacitor C will occur more slowly. As indicated in the solid-line graph of the capacitor voltage Uc in FIG. 9, the capacitor voltage builds up to a value which, at time t2 when the charging operation ends, is substantially lower than the value to which it would have built up, had there been no provision of engine-speed compensation means, i.e.. had the switch 140 remained closed during the entire charging operation. In the specific illustration of FIG. 9, it is assumed that the engine speed it 1250 rpm and that accordingly the duration of the charging operation is T /zn 240 milliseconds. If the engine-speed compensation arrangement is to be rendered inoperative at engine speeds in excess of 2000 rpm, then the time delay T3, corresponding to the discharge time of capacitor 143 in FIG. 6. should be 15 milliseconds In the embodiment just described. the charging current Ia was automatically reduced in value after elapse of time interval T; by causing transistor T15 to become non'conductive. However, an equivalent result can be achieved using the different circuit arrangement of FIG. 7.

The embodiment of FIG, 7, like that of FIG. 6, is a modification of the basic charging arrangement shown in FIG. 4. In FIG, 7, a monostable multivibrator circuit comprised of components T14 and 140-145 can again be provided, in order to generate the delay pulse of du ration T: (see FIG. 9). However, in the embodiment of FIG. 7. the collector of monostable multivibrator transistor T14 is connected, via resistor 152, with the base of a transistor T16. The emitter of T16 should be considered simply connected to the positive line 35. for the purpose of understanding the rudiments of the operation of the circuit. The base of transistor T16 is connected to positive line via resistor 153; switch 160 can be ignored or simply considered as being in open position. for the purpose of understanding the rudiments of the circuit operation. Connected to the collector of transistor T16 is an adjustable resistor 155. Transistor T16 is non-conductive whenever transistor T14 is non-conductive, i.e.. during the time interval T; if the throttle-valve-controlled switch 140 happens to be open. However, when transistor T16 is conductive, it furnishes an additional current to circuit junction M, via resistor 155, and when this additional current is furnished to junction M, the value of the charging current In decreases by the amount of this additional current.

The same corrective action can be achieved with the transistor T14, when its emitter is connected to negative line 36. if instead of the throttlevalve-controlled switch 140 use is made of another similar throttlevalve-controlled switch 160 connected in parallel to the base-emitter biasing resistor 153 of transistor T16. Switch 160, when closed, maintains transistor T16 nonconductive irrespective of the rendering conductive of transistor T14 by the voltage pulses 81 arriving from the output of bistable multivibrator 22. With transistor T16 non-conductive, the charging current la will be at its higher level Ial, so long as the throttle valve 14 is pivoted open by an angle less than 30, i.e., so long as throttlevalve-controlled switch 160 remains closed.

Instead of using switch 140, which changes the charging current value in dependence upon engine speed and throttle-valve position. and instead of using the switch 160, which changes the charging current value solely in dependence upon throttle valve position. use can be made of switches like the switches 16] and 162 shown in FIG. 7. Both these switches become closed when the throttle valve 14 is pivoted opened through an angle greater than 30. Only one of the two switches 161, 162 need be used.

FIG. 8 depicts a modification of the circuit of FIG. 6. In FIG. 8, the throttle-valve-controlled switch is replaced by a similarly controlled switch 160 connected between the positive line 35 and resistor 163. A further possibility is to permanently connect the resistor 163 to positive line 35, and replace switch 160 with a switch 161 serving to connect the emitter of transistor T14 to ground. A still further possibility is to permanently connect the emitter of transistor T14 to ground. and replace switch 161 with a throttle-valve-controlled switch 162 connected between the positive line 35 and a resistor and opened by the throttle valve when the throttle valve is pivoted open through an angle greater than 30.

The control pulse Jo generated at the collector of output transistor T6 (FIG. 2) of control monostable multivibrator 23 is applied to the pulse prolonging stage 24 which increases the duration of the control pulse by a factorf, having'a value on the order of about f= 2. The provision of the pulse prolonging stage 24 makes it easy to vary the duration Tr of the final valveopening pulse Jr in dependence upon a plurality of other engine operating conditions, such as whether the engine is being started up and requires an enriched combustion mixture, or such as whether engine is being run up requiring a control of the fuel injection in dependence upon engine temperature. Likewise, the duration of the valve-opening pulses .ll can be further varied in dependence upon engine load. or in such a manner as to maintain a predetermined fuel-air ratio, or in such a manner as to vary the fuel-air ratio in dependence upon one or more engine operating conditions.

Circuit details of a pulse-prolonging stage according to the invention are depicted in FIG. 10. The circuit of FIG. 10 is in many respects similar to the circuit of the control monostable multivibrator 23 shown in FIG. 2, and components identical to those of FIG. 2 are designated with the same reference numerals. However, the circuit of FIG. 10 differs significantly in that the multivibrator timing capacitor C in FIG. 10 is charged. not during the engine-speed-dependent period Tp n. but rather during the shorter engine-speed-dependent and air-inflow-rate-dependent duration T0 of the control impulses .lo, the charging of capacitor C in FIG. 10 being performed with a constant charging current la furnished by a source A of charging current. Immediately upon termination of control pulse .10, discharging of capacitor C in FIG. 20 commences and is performed with a constant discharging current Ie furnished by a source E of discharging current. Although the charging current la and the discharging current le for the multivibrator timing capacitor C in FIG. 10 are constant currents, it should be understood that their values are automatically adjusted in dependence upon changing engine operating conditions. These changes in current value are not very marked within a single charging or discharging operation. so that the current is in fact substantially constant; however. the changes in the magnitude of the charging current In and the discharging current le for the capacitor C of FIG. 10 become evident if a substantial number of successive charging and discharging operations are considered.

Both current sources A and E in FIG. 10 can be designed along the lines of either of the circuits in FIGS. 4 and 5. In order to realize the above-described corrective action with the current source shown in FIG. 4, the circuit stages which implement the correction of the fuel-air ratio. and which effect corrections for starting and post-starting (stages 26 and 27 in FIG. 10), must act upon the circuit junction between resistors [01 and 103 (FIG. 4). while the stage 28 for enginerun-up correction of the injected fuel quantity must act upon the emitter of transistor T9 (junction M) in FIG. 4. If the circuit shown in FIG. 4 is to be used as a discharging device. then resistor 100, transistor T10, and the collector resistor of T10 can be omitted.

The control pulse J is applied to the pulseprolonging stage 24 at the input 165 thereof FIG. Connected to input terminal 165 is the anode of a diode 166, which transmits the positive control pulse J0 to a connecting line 167, the delay pulse furnished by the pulseprolonging stage 24 being also applied to line 167 via a second diode 168 to form a composite pulse Js.

The circuit of FIG. 10, besides the elements corresponding to the circuits shown in FIGS. 2, 4 and 5, furthermore includes, for the purpose of protection against voltage breakdowns. a circuit stage comprised of two transistors T21 and T22 shorted to act like diodes. Connected in series with each other and in series with a resistor 170 connected to the negative line 36. Connected to the emitter of T22 is the base of a transistor T23 connected in Darlington configuration with a further transistor T24. The collectors of transistors T23 and T24 are connected, via timing capacitor C. with the base of transistor T2. In the stable state of the illustrated monostable circuit of FIG. 10. transistor T2 is conductive. The emitter of transistor T24 is connected in series with the discharging device E. Provision of this stage assures that, when the discharging operation is initiated. rendering transistors T1 and T11 conductive, the collector-emitter voltages of transistors T23 and T24, and the voltage on the discharging circuit E, will not be able to exceed the battery voltage on positive line 35, and accordingly the voltages applied to integrated-circuit discharge circuit E will not be able to reach dangerously high levels.

In the circuit of FIG. 10, a load-dependent stage 26 is provided. comprised of a three-position switch 171 mechanically coupled to and operated by the engine throttle valve. The movable switch member of switch 171 is connected via resistor 172 with a control input of a source A of charging current. The switching member 171 is in its illustrated open position when the throttle valve is in a position corresponding to engine idling. When the throttle valve is in a position corresponding to medium loading of the engine. the switch 171 assumes its middle position in which it connects resistor 172 to a compensating resistor 173. Resistor 173 is connected to the positive line and has a resistance such that the charging current la will have a value corresponding to lowest possible exhaust emissions. When the throttle valve is in its fully open position. swtich 171 will assume its rightmost position. to effect an increase of the charging current In to a value such as will result in a greatly enriched fuel-air mixture.

This control input of charging circuit A of FIG. 10 is furthermore connected. via diode 176 and resistor [75, to the output of a further compensating stage 27 which is automatically actuated when the engine is started and remains actuated for 20 seconds after the end of the starting operation, and is operative for raising the level of the charging current In, for purposes of fuel enrichment. Compensating stage 27 has an input 177 connected to a non-illustrated starter switch for the engine. Input 177 is connected by a resistor [78 to the base of an npn transistor T27 having an emitter connected to the negative line 36. The collector of transistor T27 is connected. via a resistor, to the base of a pnp transistor T28. Transistor T28. together with further pnp transistor T29. adjustable resistor 179 and capacitor 180. forms a Miller integrator. When the engine is started. the voltage on input terminal 177 rises to the positive supply potential. transistor T27 becomes conductive. and as a result transistors T28 and T29 are rendered conductive. This assures that a control current such as will raise the magnitude of charging current In flows to the charging current source A. via resistor I and diode 176. Furthermore, the capacitor 180 will be almost entirely discharged during the course of this compensation. At the end of the starting operation, the voltage at the input 177 of start-up compensator 27 is removed, and transistor T27 reverts to its originally non-conducting condition. In consequence of the negative feedback provided. capacitor will undergo a relatively slow charging. with the voltage at the capacitor terminal connected to the collector of transistor T29 decreasing substantially linearly towards the voltage on the negative line 36.

The magnitude of the charging current is dependent upon the setting of the adjustable resistor I79 connected between the base of transistor T28 and the positive line 35. and corresponds to the quotient of the sum of the two base-emitter voltages of transistors T28. T29 and the resistance of resistor 179. In this manner. it is possible to adjust the duration of the post-starting fuel enrichment in a very precise manner. this compensation period ending when the potential applied to source A by resistor and diode 176 falls below a threshold voltage established at the control input of source A. so that diode I76 becomes non-conductive. During this time period. the post-starting enrichment adjustable via resistor 175 continuously decreases.

The circuit of FIG. 10 furthermore includes a temperature-compensation stage 28 connected not to charging circuit A. but instead to discharging circuit E. Temperaturecompensation stage 28 comprises a negativetemperature-coefficient resistor [82 maintained in heat-exchanging relationship with the cooling fluid in the engine cooling system. NTC resistor 182, together with an adjustable resistor 183, a diode 184 and a second adjustable resistor. form a voltage divider connected between the positive and negative supply lines 35, 36. The junction between resistor 185 and diode 184 is connected to the base of an npn transistor T30 having a collector connected to the positive line 35, and having an emitter connected to the negative line 36 via a resistor 186. The emitter of transistor T30 is connected. via a third adjustable resistor 187 and a further diode 188. to the control input of a discharging circuit F. The NTC resistor 182 has the effect of increasing the magnitude of the discharge current It as the tempera ture of the engine rises. so that as the engine temperature rises the duration of the discharging operation decreases. resulting in a decrease of the prolonging factor fdiscussed earlier.

If all the engine operating conditions remain constant. the actual period of time for which the fuelinjection valves are opened might vary as a function of variations in the battery supply voltage. unless suitable compensating measures are taken. ln particular. the finite and different pull-in and drop-out times of the electromagnetic valves must be taken into account. and in particular the relationship between such pull-in and drop-out times and changes in the voltage applied across the valve solenoids. The voltage compensation stage shown in FIG. 1 is provided to effect the necessary compensation. Specifically. compensation stage 25 prolongs the duration Tv of the valve-opening pulses in an additive manner, in response to changes of battery voltage, so that when the battery voltage decreases. the duration T1 of the valve-opening pulses .lv will be increased by an amount equal to the corresponding increase in the time required for the valve to actually open in response to the lowermagnitude valveopening voltage pulse. The time for the valve to return to its closed condition is shorter than the opening time. and is by comparison independent of variations in battery voltage.

Circuit details of an exemplary version of the voltagecompensation stage 25 of FIG. 1 are depicted in FIG. 11.

The circuit of FIG. 11 includes two diodes 166. 168 joined at their cathodes to form an OR-gate. These cathodes are connected via resistor 190 to the base of an npn transistor T31, this base being connected to the negative line 36 by a base-emitter biasing resistor 191. The emitter of transistor T3l is directly connected to the negative line 36. The collector of transistor T31 is connected to positive line via a collector resistor 192. and is furthermore connected to the base of an npn transistor T32. The emitter of transistor T32 is connected directly to the negative line 36. A resistor 193 connects the collector of T32 to the emittor of a transistor T33 which acts like a Zener diode due to the short-circuiting of its base-collector path. The emitter of T33 is furthermore connected to the positive line 35 via a resistor [94. The base and collector of T33 are connected tc the negative line 36 by way of two diodes, formed by transistors T34 and T35 likewise having short-circuited base-collector paths. However. while transistor T33 is reverse-biased in Zener-diode fashion. transistors T34 and T35 are forward-biased.

Connected to the emitter of T33 are both the base and collector of a further transistor T36 which acts like a forward-biased diode. The emitter of T36, and also the emitter of a further transistor T37. are connected to the negative line 36 by a capacitor 195. An adjustable resistor 196 is connected in parallel with capacitor 195. The base of transistor T37 is connected to the voltage-divider tap of voltage-divider 197, 198. The collector of T37 is connected to the base of a pnp transistor T38. The emitter of T38 is directly connected to positive line 35, and the collector of T38 is connected. via a resistor 20]. with the cathode of a diode 202 and with the base of an npn transistor T39. The base of T39 is connected to negative line 36 by a resistor 203. The

collector of 139 is connected to positive line 35 by a resistor 204. and is furthermore connected to the base of a transistor T40 having an emitter directly Con nected to negative line 36. The collector of T40 is connected to the positive line 35 via series-connectcd resistors 205 and 206. as is also the collector of transistor T4]. The base of T41 is connected via a resistor 207 to the connecting line 167. Connecting line 167 transmits the pulse Js.

The junction of resistors 205. 206 is connected to the base of a pnp transistor T42. whose emitter is connected to the negative line 36 via three seriesconnected resistors 208, 209 and 210. The collector of T42 is connected to the base of an npn emitter-follower transistor T43. The collector of T43 is directly connected to positive line 35, and the emitter of T43 is connected to the negative line 36 by two seriesconnected resistors 211, 212. Connected to the junction between resistors 211 and 212 is a pulsetransmitting output line 213. Line 213 transmits to the input of the power amplification stage 10 the delay pulse derived from the control pulse Jo by the pulseprolonging stage 24 and the valve-opening pulse .lv furnished from the voltage-compensation stage 25.

The junction between resistors 209 and 210 is connected to the base of a transistor T44. The collector of T44 is connected to the anode of diode 202, and is furthermore connected via resistor 215 to the positive line 35.

The pulse .ls. comprised of the control pulse Jo of control monostable multivibrator 23 and the prolonging pulse furnished by the pulse-prolonging stage 24, is transmitted via resistor from the cathodes of diodes 166. 168 to the base of transistor T31. which becomes conductive for the duration of this pulse. When T31 is conductive. T32 is non-conductive. and accordingly T32 conducts only during the intervals between the pulses .15. With T32 non-conductive, capacitor can charge up to the temperature reference voltage drop between the base of T36 and the negative line 36. As a result. the emitter voltage of transistor T37 increases. relative to the voltage established at its base by resistors 197, 198. so that the transistor T37 and also transistor T38 become non-conductive. Transistor T39 becomes non-conductive only when transistor T44 is conductive. i.e.. so long as a pulse is present on pulsetransmitting line 167. Such a pulse simultaneously renders transistors T42 and T43 conductive. Because the transistor T39 is non-conductive and the transistor T40 is conductive, any small time separation between the trailing edge of control pulse 10 and the leading edge of the prolonging pulse, which is added to Jo to form .15. will not make itself evident at the output pulsetransmitting line 213.

Immediately at the end of pulse Js. transistors T31 and T32 become conductive. and the diode formed by transistor T36 becomes non-conductive. The capacitor 195, which has meanwhile charged up to the batteryvoltage-indcpendent reference voltage, can now discharge. through resistor 196. down to a voltage proportional to the battery voltage and established by voltage divider 197, 198. The time required for this discharge to take place is accordingly dependent upon the battery voltage. At the end of this discharge, transistor T37, and accordingly transistors T38 and T39, become conductive. whereas transistors T40. T42 and T43 become non-conductive At this moment the \ahe-opening pulse Jr comes to an end.

The diode 202 and the transistor T44 together with the transistor T3) pre\ent the voltage pulse generated across the valve solenoids when they become dcenergized from triggering anew the voltage-compensation stage 25.

In the block diagram of FIG. 1. a pulse-durationlimiting stage 29 is connected in parallel with the frequencydi\ iding bistable multixibrator 22 and the control monostable multivibrator 23. Limiting stage 29 prevents the generation of excessively long valve-opening pulses .lv. hieh could occur as a result of mechanical or electrical failure. for example as a result of an accidental short-circuiting to ground of the junction H of potentiometer 17, or as a result of an interruption in the continuity of the connection to voltage supply line 35. Specifically. limiting stage 29 prevents the generation ofa control pulse having a duration greater than 4.5 milliseconds. To this end, the duration of the astable state of pulse-shaping monostable multivibrator 22 is chosen to be 4.5 milliseconds, so as to obviate the necessity for a further timing stage to generate a timing pulse having that duration. The limiting of the pulse duration of control pulse .10 is effected by transistor 45 (FIG. 2). The collector of transistor 45 is connected to the collector of output transistor T6, the collector of T6 constituting the output of control monostable multivibrator 23. Transistors 45 and 44 (FIG. 2), as already explained, together form a monostable multivibrator. and asjust mentioned the duration of the unstable state of this multivibrator is 45 milliseconds. While this monostable multivibrator is in its unstable state, transistor 45 is non-conductive. However, upon elapse of the mentioned 4.5 milliseconds, transistor 45 again becomes conductive, and thereby short-circuits to ground the collector of output transistor T6 of control monostable multivibrator 23. In this way, an upper limit of 4.5 milliseconds is established for the duration of the pulse Jo produced at the collector of output transistor T6.

The circuit of FIG. 5 is a merely exemplary, but preferred circuit, for the discharge circuit E of multivibra tor 23 in FIG. 2. The potentiometer 17 in FIG. 5, whose wiper 16 is moved by the pivotable airflow sensing member 15, is provided with three taps, spaced along its length. Four resistors 148, 149, 150 and 151 are each connected in parallel with a respective one of the four portions of potentiometer 17 defined by the three justmentioned taps. The resistances of resistors 14845] are so chosen as to establish a substantially exponential relationship between the angular displacement of the airflow sensing member and the voltage taken off the potentiometer wiper 16. To more closely synthesize the desired exponential relationship, an additional loading resistor 130 is connected between the potentiometer wiper 16 and the circuitjunction H. Provision of resistor 130 smooths the transitions between the different sections of the potentiometer.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in an electronic arrangement for controlling the amount of fuel injected into an engine cylinder in dependence upon the air inflow rate and other engine operating conditions. it is not to be con sidered limited to the details shown. since various structural and circuit modifications may be made without departing in any way from the spirit and concept of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various purposes without omitting features that from the standpoint of prior art fairly constitute essential aspects of the generic or specific features of this invention and, therefore, such modifications should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is set forth in the appended claims 1. In an internal-combustion engine having at least one engine cylinder, an air-intake passage communicating with the interior of such cylinder, a piston movable in such cylinder, an engine crankshaft connected to such piston, an ignition arrangement for igniting fuel-air mixture in such cylinder and including electromechanical ignition-signal generating means coupled to the engine crankshaft and operative for generating a train of electrical crankshaft-positionsynchronized ignition signals, and an electrically actuatable fuelinjection valve having an electrical input for receipt of a valve-opening pulse and operative for injecting fuel into such cylinder for a time interval corresponding to the duration of such valve-opening pulse. for use therewith, a fuel-injection control system comprising airflows sensing means for determining the rate of airflow through the air-intake passage of the engine; triggering means including electronic frequency divider means for receiving the train of electrical ignition signals and converting the same into a lower-frequency train of electrical fuel-injection triggering pulses; first pulsegenerating means connected to said triggering means and to said airflow sensing means and operative for generating a first control pulse having a pulse duration dependent upon the airflow rate detected by said airflow sensing means; second pulse-generating means connected to said triggering means and to said first pulse-generating means and operative upon generation of a triggering pulse for generating a second control pulse having a pulse duration dependent upon at least one other variable engine operating condition; and third means for generating a composite valve-opening pulse comprised of said first and second control pulses for application to the electrical input of the fuelinjection valve.

2. A system as defined in claim 1, wherein said second pulse-generating means consists of means con nected to said triggering means and to said first pulsegenerating means and operative for generating said second control pulse upon termination of said first control pulse, and wherein said third means means for generating valve a composite valve-opening pulse comprised of said first and second control pulses and having a total duration greater than the duration of said first control pulse and greater than the duration of said second control pulse.

3. A system as defined in claim 1, wherein said first and second pulse-generating means are comprised of respective pulse-generating circuits and a voltage supply connected to said pulse-generating circuits for furnishing electrical energy to the latter and to the electrical input of the fuel-injection valve; and further comprising voltage-compensation means operative for counteracting the effect of variations in the output of said voltage supply upon the time interval the fuel injection valve remains open by varying the duration of said valve-opening pulse in dependence upon variations in the output of said voltage supply.

4. A system as defined in claim 3, wherein said voltage-compensation means comprises a voltage divider connected across said voltage supply and having a voltage-divider tap at which appears a voltage directly indicative of the voltage across said voltage supply, a timing capacitor, means operative upon receipt of said second pulse for charging said timing capacitor to a predetermined voltage, and including Zener diode means connected across said timing capacitor to assure a precise value for the timing capacitor voltage and operative upon termination of said second pulse for causing said timing capacitor to discharge, transistor comparator means having one input connected to said voltage divider tap and having another input connected to said timing capacitor and operative for detecting the difference between the voltage across said timing capacitor and the voltage across said voltage supply and operative during discharge of said timing capacitor for generating a voltage supply compensating pulse having a duration dependent upon the voltage across said voltage supply, and wherein said means for applying a composite valve-opening pulse comprises means for combining said first and second control pulses and said compensating pulse to form said valve-opening pulse.

5. A system as defined in claim 4, wherein said Zener diode means is comprised of a transistor having a shortcircuited base-collector path and connected to conduct in breakdown direction and thereby act as a Zener diode and in series therewith at least one further transistor having a short-circuited base-collector path and connected to conduct in forward-bias direction and thereby act as a forward-biased diode.

6. A system as defined in claim 5, wherein said transistor comparator means comprises a transistor having a base connected to said 'oltage-dividcr tap and an emitter connected to said timing capacitor, and wherein said means for combining said first, second and compensating pulses comprises a transistor having a conductivity type complementary to the conductivity type of said transistor of said transistor comparator means and having a base connected to the collector of said transistor of said transistor comparator means and having an emitter-collector path connected across said voltage supply.

7. A system as defined in claim 4. wherein said voltage-compensation means further comprises two OR-gate transistors having joined collectors and joined emitters, a shared collector resistor connected in series with the parallel connection of the collector-emitter paths of said two OR-gate transistors, the shared collec tor resistor and parallel collector-emitter paths being connected across said voltage supply, means for applying to the base of one of said OR-gate transistors a composite pulse comprised of said first and second control pulses and means for applying to the base of the other of said OR-gate transistors said voltage-supply compensating pulse.

8. A system as defined in claim 7, wherein said voltage-compensation means additionally comprises a further transistor having a base-emitter path connected in parallel with said shared collector resistor, an emitter-follower transistor having a base connected to the collector of said further transistor and having a collector connected to one terminal of said voltage supply and having an emitter, means connecting the emitter of said emitter-follower transistor to the other terminal of said voltage supply, a plurality of seriesconnected resistors connecting the collector of said further transistor to said other terminal of said voltage supply, a feedback transistor having a base connected to the junction between two adjoining ones of said plurality of seriesconnccted resistors and having an emitter connected to one of said terminals of said voltage supply and having a collector, and a feedback diode connecting the collector of said feedback transistor to the base of said other of said OR-gatc transistors.

9. A system as defined in claim I, wherein said first pulse generating means comprises first timing capacitor means, means for effecting a first change of stored energy of said first capacitor means in response to generation of a triggering signal by said triggering means for a time interval corresponding to the rotation of said crankshaft through a fixed predetermined angle, and means for effecting an opposite second change of stored energy of said first capacitor means in response to generation of a subsequent triggering signal by said triggering means, at least one of said means for effecting a change of stored energy of said first capacitor means comprising means for effecting such change of stored energy in dependence upon the airflow rate detected by said airflow sensing means. and wherein said first pulse generating means is operative for generating said first control pulse during the time period of said second change of stored energy of said first capacitor means.

10. A system as defined in claim 9, wherein said means for effecting a first change of stored energy of said first capacitor means comprises means for charging said first capacitor means for a time interval corresponding to the intervals between triggering pulses and accordingly to a fixed predetermined angle of crankshaft rotation, and wherein said means for effecting an opposite second change of stored energy of said first capacitor means comprises means for discharging said first capacitor means at a rate varying inversely to the airflow rate detected by said airflow sensing means.

ll. A system as defined in claim 10, wherein said means for discharging said first capacitor means comprises means for discharging said first capacitor means at a rate inversely proportional to the airflow rate detected by said airflow sensing means.

12. A system as defined in claim 1, wherein said frequency divider means comprises bistable multivibrator means operative for halving the frequency of the train of ignition signals.

13. A system as defined in claim 12, wherein said bistable multivibrator means has two outputs and has an input and operates in such a manner that a first one of said two outputs of said bistable multivibrator means becomes actuated in response to every second triggering pulse.

14. A system as defined in claim 13, wherein said first pulse-generating means comprises a control monostable multivibrator circuit, said control monostable multivibrator circuit comprising timing capacitor means. a first voltage supply line and a second voltage supply line. a first monostable multivibrator transistor having an emitter connected to said first voltage supply line. a differentiating element connecting the base of said first transistor to said first output of said bistable multivibrator means, and the collector of said transistor being connected to a first terminal of said timing capacitor means, a second monostable multivibrator transistor of the same conductivity type as said first transistor having an emitter connected to said first voltage supply line, having a base connected to the second terminal of said timing capacitor means, a third monostable multivibrator transistor of conductivity type opposite to the conductivity type of said first and second transistors and having a collector connected to the base of said first transistor by means of a connecting resistor and having an emitter connected to said second voltage supply line and having a base connected to the second one of the two outputs of said bistable multivibrator means.

15. A system as defined in claim 14, wherein said control monostable multivibrator further comprises a fourth monostable multivibrator transistor of the same conductivity type as said third transistor and having an emitter connected to said second voltage supply line and having a base connected via a connecting resistor to said second voltage supply line, a resistor connecting said base of said fourth transistor to the collector of said second transistor. a resistor connecting said base of said fourth transistor to said first output of said bistable multivibrator means, a resistor connecting the collector of said fourth transistor with said first voltage supply line, and means connecting the collector of said fourth transistor to the base of said third transistor.

16. A system as defined in claim 15, wherein said control monostable multivibrator includes adjustable constant-current charging means operative for charging said timing capacitor means and adjusting means connected to said charging means and to said airflow sensing means and operative for adjusting the charging current furnished by said constant-current charging means in dependence upon the airflow rate detected by said airflow sensing means.

17. A system as defined in claim 15, wherein said control monostable multivibrator includes adjustable constant-current discharging means operative for discharging said timing capacitor means and adjusting means connected to said discharging means and to said airflow sensing means and operative for adjusting the level of the discharging current furnished by said constant-current discharging means in dependence upon the airflow rate detected by said airflow sensing means.

18. A system as defined in claim 15, wherein said control monostable multivibrator comprises charging means for charging said timing capacitor means and discharging means for discharging said timing capacitor means, at least one of said charging and discharging means comprising operational amplifier means having an output connected to said timing capacitor means and having input means and means for controlling the current flow through said timing capacitor means by controlling the voltage at the output of said operational amplifier means.

19. A system defined in claim 15, wherein said control monostable multivibrator comprises charging means for charging said timing capacitor means and discharging means for discharging said timing capacitor means, at least one of said charging and discharging means comprising an operational amplifier circuit comprising an operational amplifier having an output and having input means, a Darlington transistor circuit having an input connected to the output of said operational amplifier and having an output current path connected to said timing capacitor means for carrying capacitor current. and means connected to said input means of said operational amplifier for controlling the flow of current through said timing capacitor means by controlling the flow of current through said output current path of said Darlington transistor circuit.

20. A system as defined in claim 19, wherein said operational amplifier circuit further comprises a compensating capacitor connected between one output terminal of said Darlington transistor circuit and said operational amplifier, and wherein said operational amplifier has an inverting input and a non-inverting input, and wherein said operational amplifier circuit further includes voltage follower means having an input connected to said non-inverting input and having an output connected to said inverting input of said operational amplifier and operative for maintaining the voltage across said compensating capacitor substantially constant at a predetermined value when said Darlington transistor circuit conducts timing capacitor means current and at substantially the same predetermined value when said Darlington transistor circuit does not conduct timing capacitor means current.

21. A system defined in claim 20, wherein said voltage follower means comprises a compensating transistor having a base, an emitter and a collector. and wherein said operational amplifier circuit further comprises a voltage divider connected across said first and second voltage supply lines and comprised of three resistors connected in series with each other with the middle one of said three resistors having one terminal connected to the base of said compensating transistor and another terminal connected to said noninverting input of said operational amplifier.

22. A system as defined in claim 21. wherein the emitter of said compensating transistor is connected to said inverting input of said operational amplifier and to said output terminal of said Darlington transistor circuit.

23. A system as defined in claim 19. wherein said operational amplifier circuit serves to discharge said timing capacitor means and is comprised of a second operational amplifier, in addition to the first operational amplifier, said second operational amplifier having an output, a non-inverting input and an inverting input, and the first operational amplifier having a noninverting input and an inverting input, and wherein said airflow sensing means comprises potentiometer means having a movable wiper, and mechanical airflowresponsive means for moving said wiper in dependence upon the airflow rate through said air-intake passage, said non-inverting input of said second operational amplifier being connected to said wiper. a voltage divider connected across said first and second voltage supply lines and having a voltage-divider tap connected to the non inverting input of said first operational amplifier.

24. A system as defined in claim 23, and further including a discharging resistor having a first terminal connected to said output terminal of said Darlington transistor circuit and having a second terminal connected to the output of said second operational amplifier, the output of said second operational amplifier being connected to said inverting input thereof, and 

1. In an internal-combustion engine having at least one engine cylinder, an air-intake passage communicating with the interior of such cylinder, a piston movable in such cylinder, an engine crankshaft connected to such piston, an ignition arrangement for igniting fuel-air mixture in such cylinder and including electromechanical ignition-signal generating means coupled to the engine crankshaft and operative for generating a train of electrical crankshaft-positionsynchronized ignition signals, and an electrically actuatable fuel-injection valve having an electrical input for receipt of a valve-opening pulse and operative for injecting fuel into such cylinder for a time interval corresponding to the duration of such valve-opening pulse, for use therewith, a fuel-injection control system comprising airflows sensing means for determining the rate of airflow through the air-intake passage of the engine; triggering means including electronic frequency divider means for receiving the train of electrical ignition signals and converting the same into a lower-frequency train of electrical fuel-injection triggering pulses; first pulse-generating means connected to said triggering means and to said airflow sensing means and operative for generating a first control pulse having a pulse duration dependent upon the airflow rate detected by said airflow sensing means; second pulse-generating means connected to said triggering means and to said first pulse-generating meAns and operative upon generation of a triggering pulse for generating a second control pulse having a pulse duration dependent upon at least one other variable engine operating condition; and third means for generating a composite valve-opening pulse comprised of said first and second control pulses for application to the electrical input of the fuel-injection valve.
 2. A system as defined in claim 1, wherein said second pulse-generating means consists of means connected to said triggering means and to said first pulse-generating means and operative for generating said second control pulse upon termination of said first control pulse, and wherein said third means means for generating valve a composite valve-opening pulse comprised of said first and second control pulses and having a total duration greater than the duration of said first control pulse and greater than the duration of said second control pulse.
 3. A system as defined in claim 1, wherein said first and second pulse-generating means are comprised of respective pulse-generating circuits and a voltage supply connected to said pulse-generating circuits for furnishing electrical energy to the latter and to the electrical input of the fuel-injection valve; and further comprising voltage-compensation means operative for counteracting the effect of variations in the output of said voltage supply upon the time interval the fuel-injection valve remains open by varying the duration of said valve-opening pulse in dependence upon variations in the output of said voltage supply.
 4. A system as defined in claim 3, wherein said voltage-compensation means comprises a voltage divider connected across said voltage supply and having a voltage-divider tap at which appears a voltage directly indicative of the voltage across said voltage supply, a timing capacitor, means operative upon receipt of said second pulse for charging said timing capacitor to a predetermined voltage, and including Zener diode means connected across said timing capacitor to assure a precise value for the timing capacitor voltage and operative upon termination of said second pulse for causing said timing capacitor to discharge, transistor comparator means having one input connected to said voltage divider tap and having another input connected to said timing capacitor and operative for detecting the difference between the voltage across said timing capacitor and the voltage across said voltage supply and operative during discharge of said timing capacitor for generating a voltage-supply compensating pulse having a duration dependent upon the voltage across said voltage supply, and wherein said means for applying a composite valve-opening pulse comprises means for combining said first and second control pulses and said compensating pulse to form said valve-opening pulse.
 5. A system as defined in claim 4, wherein said Zener diode means is comprised of a transistor having a short-circuited base-collector path and connected to conduct in breakdown direction and thereby act as a Zener diode and in series therewith at least one further transistor having a short-circuited base-collector path and connected to conduct in forward-bias direction and thereby act as a forward-biased diode.
 6. A system as defined in claim 5, wherein said transistor comparator means comprises a transistor having a base connected to said voltage-divider tap and an emitter connected to said timing capacitor, and wherein said means for combining said first, second and compensating pulses comprises a transistor having a conductivity type complementary to the conductivity type of said transistor of said transistor comparator means and having a base connected to the collector of said transistor of said transistor comparator means and having an emitter-collector path connected across said voltage supply.
 7. A system as defined in claim 4, wherein said voltage-compensation means further comprises two OR-gate transistors having joined collectors and joined emitters, a shared collector resistor connected in series with the parallel connection of the collector-emitter paths of said two OR-gate transistors, the shared collector resistor and parallel collector-emitter paths being connected across said voltage supply, means for applying to the base of one of said OR-gate transistors a composite pulse comprised of said first and second control pulses and means for applying to the base of the other of said OR-gate transistors said voltage-supply compensating pulse.
 8. A system as defined in claim 7, wherein said voltage-compensation means additionally comprises a further transistor having a base-emitter path connected in parallel with said shared collector resistor, an emitter-follower transistor having a base connected to the collector of said further transistor and having a collector connected to one terminal of said voltage supply and having an emitter, means connecting the emitter of said emitter-follower transistor to the other terminal of said voltage supply, a plurality of series-connected resistors connecting the collector of said further transistor to said other terminal of said voltage supply, a feedback transistor having a base connected to the junction between two adjoining ones of said plurality of series-connected resistors and having an emitter connected to one of said terminals of said voltage supply and having a collector, and a feedback diode connecting the collector of said feedback transistor to the base of said other of said OR-gate transistors.
 9. A system as defined in claim 1, wherein said first pulse generating means comprises first timing capacitor means, means for effecting a first change of stored energy of said first capacitor means in response to generation of a triggering signal by said triggering means for a time interval corresponding to the rotation of said crankshaft through a fixed predetermined angle, and means for effecting an opposite second change of stored energy of said first capacitor means in response to generation of a subsequent triggering signal by said triggering means, at least one of said means for effecting a change of stored energy of said first capacitor means comprising means for effecting such change of stored energy in dependence upon the airflow rate detected by said airflow sensing means, and wherein said first pulse generating means is operative for generating said first control pulse during the time period of said second change of stored energy of said first capacitor means.
 10. A system as defined in claim 9, wherein said means for effecting a first change of stored energy of said first capacitor means comprises means for charging said first capacitor means for a time interval corresponding to the intervals between triggering pulses and accordingly to a fixed predetermined angle of crankshaft rotation, and wherein said means for effecting an opposite second change of stored energy of said first capacitor means comprises means for discharging said first capacitor means at a rate varying inversely to the airflow rate detected by said airflow sensing means.
 11. A system as defined in claim 10, wherein said means for discharging said first capacitor means comprises means for discharging said first capacitor means at a rate inversely proportional to the airflow rate detected by said airflow sensing means.
 12. A system as defined in claim 1, wherein said frequency divider means comprises bistable multivibrator means operative for halving the frequency of the train of ignition signals.
 13. A system as defined in claim 12, wherein said bistable multivibrator means has two outputs and has an input and operates in such a manner that a first one of said two outputs of said bistable multivibrator means becomes actuated in response to every second triggering pulse.
 14. A system as defined in claim 13, wherein said first pulse-generating means comprises a control monostable multivibrator circuit, said control monostable multivIbrator circuit comprising timing capacitor means, a first voltage supply line and a second voltage supply line, a first monostable multivibrator transistor having an emitter connected to said first voltage supply line, a differentiating element connecting the base of said first transistor to said first output of said bistable multivibrator means, and the collector of said transistor being connected to a first terminal of said timing capacitor means, a second monostable multivibrator transistor of the same conductivity type as said first transistor having an emitter connected to said first voltage supply line, having a base connected to the second terminal of said timing capacitor means, a third monostable multivibrator transistor of conductivity type opposite to the conductivity type of said first and second transistors and having a collector connected to the base of said first transistor by means of a connecting resistor and having an emitter connected to said second voltage supply line and having a base connected to the second one of the two outputs of said bistable multivibrator means.
 15. A system as defined in claim 14, wherein said control monostable multivibrator further comprises a fourth monostable multivibrator transistor of the same conductivity type as said third transistor and having an emitter connected to said second voltage supply line and having a base connected via a connecting resistor to said second voltage supply line, a resistor connecting said base of said fourth transistor to the collector of said second transistor, a resistor connecting said base of said fourth transistor to said first output of said bistable multivibrator means, a resistor connecting the collector of said fourth transistor with said first voltage supply line, and means connecting the collector of said fourth transistor to the base of said third transistor.
 16. A system as defined in claim 15, wherein said control monostable multivibrator includes adjustable constant-current charging means operative for charging said timing capacitor means and adjusting means connected to said charging means and to said airflow sensing means and operative for adjusting the charging current furnished by said constant-current charging means in dependence upon the airflow rate detected by said airflow sensing means.
 17. A system as defined in claim 15, wherein said control monostable multivibrator includes adjustable constant-current discharging means operative for discharging said timing capacitor means and adjusting means connected to said discharging means and to said airflow sensing means and operative for adjusting the level of the discharging current furnished by said constant-current discharging means in dependence upon the airflow rate detected by said airflow sensing means.
 18. A system as defined in claim 15, wherein said control monostable multivibrator comprises charging means for charging said timing capacitor means and discharging means for discharging said timing capacitor means, at least one of said charging and discharging means comprising operational amplifier means having an output connected to said timing capacitor means and having input means and means for controlling the current flow through said timing capacitor means by controlling the voltage at the output of said operational amplifier means.
 19. A system as defined in claim 15, wherein said control monostable multivibrator comprises charging means for charging said timing capacitor means and discharging means for discharging said timing capacitor means, at least one of said charging and discharging means comprising an operational amplifier circuit comprising an operational amplifier having an output and having input means, a Darlington transistor circuit having an input connected to the output of said operational amplifier and having an output current path connected to said timing capacitor means for carrying capacitor current, and means connected to said input means of said operational amplifier for coNtrolling the flow of current through said timing capacitor means by controlling the flow of current through said output current path of said Darlington transistor circuit.
 20. A system as defined in claim 19, wherein said operational amplifier circuit further comprises a compensating capacitor connected between one output terminal of said Darlington transistor circuit and said operational amplifier, and wherein said operational amplifier has an inverting input and a non-inverting input, and wherein said operational amplifier circuit further includes voltage follower means having an input connected to said non-inverting input and having an output connected to said inverting input of said operational amplifier and operative for maintaining the voltage across said compensating capacitor substantially constant at a predetermined value when said Darlington transistor circuit conducts timing capacitor means current and at substantially the same predetermined value when said Darlington transistor circuit does not conduct timing capacitor means current.
 21. A system as defined in claim 20, wherein said voltage follower means comprises a compensating transistor having a base, an emitter and a collector, and wherein said operational amplifier circuit further comprises a voltage divider connected across said first and second voltage supply lines and comprised of three resistors connected in series with each other with the middle one of said three resistors having one terminal connected to the base of said compensating transistor and another terminal connected to said non-inverting input of said operational amplifier.
 22. A system as defined in claim 21, wherein the emitter of said compensating transistor is connected to said inverting input of said operational amplifier and to said output terminal of said Darlington transistor circuit.
 23. A system as defined in claim 19, wherein said operational amplifier circuit serves to discharge said timing capacitor means and is comprised of a second operational amplifier, in addition to the first operational amplifier, said second operational amplifier having an output, a non-inverting input and an inverting input, and the first operational amplifier having a non-inverting input and an inverting input, and wherein said airflow sensing means comprises potentiometer means having a movable wiper, and mechanical airflow-responsive means for moving said wiper in dependence upon the airflow rate through said air-intake passage, said non-inverting input of said second operational amplifier being connected to said wiper, a voltage divider connected across said first and second voltage supply lines and having a voltage-divider tap connected to the non-inverting input of said first operational amplifier.
 24. A system as defined in claim 23, and further including a discharging resistor having a first terminal connected to said output terminal of said Darlington transistor circuit and having a second terminal connected to the output of said second operational amplifier, the output of said second operational amplifier being connected to said inverting input thereof, and said one output terminal of said Darlington transistor circuit being connected to said inverting input of said first operational amplifier.
 25. A system as defined in claim 1, wherein said first pulse generating means comprises a monostable multivibrator including timing capacitor means and charging means operative in response to a triggering pulse for charging said timing capacitor means for a charging time interval corresponding to the interval between triggering pulses and accordingly to the rotation of the crankshaft through a predetermined fixed angle, said charging means comprising means for charging said timing capacitor means during a fixed-duration predetermined first portion of said charging time interval with a constant charging current having a first value, and means for charging said timing capacitor means during a predeterminEd second portion of said charging time interval with a constant charging current having a different second value, and means operative in response to the subsequent triggering pulse generated by said triggering means for discharging said timing capacitor means at a rate varying inversely to the airflow rate detected by said airflow sensing means.
 26. A system as defined in claim 25, wherein said first portion of said charging time interval has a fixed duration approximately equal to the time required for said crankshaft to turn through said predetermined fixed angle when the crankshaft rotational speed is approximately 2500 rpm, and wherein said first value is higher than said second value.
 27. A system as defined in claim 25, wherein said engine further comprises a throttle valve located in said air-intake passage, and wherein said first pulse-generating means comprises overriding means for preventing a change of said timing capacitor means charging current from said first value to said second value except when the throttle valve is opened to a predetermined extent.
 28. A system as defined in claim 1, wherein said first pulse generating means comprises a monostable multivibrator including timing capacitor means, means operative in response to the generation of a triggering pulse by said triggering means for charging said timing capacitor means for a charging time interval corresponding to the time interval between triggering pulses and accordingly to the rotation of the crankshaft through a predetermined fixed angle, and means operative in response to the generation of a subsequent triggering pulse by said triggering means for discharging said timing capacitor means at a rate varying inversely to the airflow rate detected by said airflow sensing means, and a plurality of monostable multivibrator means connected to said means for charging said timing capacitor means and operative during their respective unstable states for maintaining the timing capacitor means charging current at different respective values.
 29. A system as defined in claim 1, wherein said second pulse generating means comprises a timing circuit comprising timing capacitor means, means connected to said first pulse generating means and operative for the duration of said first control pulse for effecting a first change of stored energy of said timing capacitor means, and means connected to said first pulse generating means and operative upon termination of said first control pulse for effecting an opposite second change of stored energy of said timing capacitor means lasting until the voltage across said timing capacitor means reaches a predetermined value, and means for generating said second control pulse during said second change of stored energy of said timing capacitor means.
 30. A system as defined in claim 29, wherein at least one of said means for effecting said first and second changes of stored energy comprises a constant current source.
 31. A system as defined in claim 29, wherein both said means for effecting said first and second change of stored energy comprise constant-current sources.
 32. A system as defined in claim 29, wherein at least one of said means for effecting said first and second changes of stored energy comprises an adjustable constant-current source and means for adjusting said adjustable constant-current source in dependence upon at least one variable engine operating condition.
 33. A system as defined in claim 29, wherein said means for effecting said second change of stored energy has a path for the flow of timing capacitor means current, and further including a transistor having a collector-emitter path connected in series with said timing capacitor means and in series with said path for the flow of timing capacitor means current and having a base, and voltage-divider means having a voltage-divider tap connected to said base, said voltage divider means including forward-biased diode means.
 34. A system as defined in claim 33, further comprising a further transistor connected with the first-mentioned transistor in Darlington configuration, said voltage-divider tap being connected to the base of said further transistor.
 35. A system as defined in claim 33, wherein said voltage divider means includes an ohmic resistor and the collector-emitter paths of transistors having short-circuited base-collector paths.
 36. A system as defined in claim 29, wherein said means for effecting said first change of stored energy comprises a current path connected to said timing capacitor means for the flow of timing capacitor means current, and wherein said second pulse generating means comprises a first voltage supply line and a second voltage supply line, a first transistor having a collector-emitter path connected between said first voltage supply line and one terminal of said path for the flow of timing capacitor means current, a resistor connecting the base of said first transistor to said first voltage supply line, differentiating means connecting the base of said first transistor to the output of said first pulse generating means for applying to the base of said first transistor a forward-bias voltage corresponding substantially to the time derivative of said first control pulse, a second transistor having a collector connected to the base of said first transistor, a resistor connecting the base of said second transistor to said second voltage supply line, a third transistor constituting the output transistor of said second pulse-generating means and having a collector connected to said first voltage supply line and an emitter connected to the base of said second transistor, and means connected to the base of said third transistor and to said timing capacitor means and operative for controlling the conductivity of said third transistor in dependence upon the voltage across said timing capacitor means.
 37. A system as defined in claim 36, wherein said means for controlling the conductivity of said third transistor comprises a fourth transistor having a collector-emitter path connected between the base of said third transistor and one of said voltage supply lines and operative for controlling the conductivity of said third transistor, and means connecting the base of said fourth transistor to the output of said first pulse generating means for controlling the conductivity of said fourth transistor and thereby the conductivity of said third transistor for the duration of said first control pulse.
 38. A system as defined in claim 37, said means for effecting a first change of stored energy of said timing capacitor means including a current path for the flow of timing capacitor means current with such current path having a terminal connected to a terminal of said timing capacitor means, and wherein said second pulse generating means further includes a fifth transistor having an emitter connected to said first voltage supply line and having a collector, means connecting the collector of said fifth transistor to the base of said fourth transistor for controlling the conductivity of said fourth transistor in dependence upon the conductivity of said fifth transistor, said fifth transistor having a base connected to that one of the two terminals of said timing capacitor means which is connected to said means for effecting said second change of stored energy.
 39. A system as defined in claim 29, wherein at least one of said means for effecting said first and said second changes of stored energy of said timing capacitor means comprises an operational amplifier circuit including an operational amplifier having an output connected to said timing capacitor means and having input means and means connected to said input means of said operational amplifier and operative for controlling the flow of current through said timing capacitor means by controlling the voltage at the output of said operational amplifier.
 40. A system as defined in claim 29, said engine comprising a throttle valve positioned in said air-intake passage, and wherein at least one of said means for effecting said first and second changes of stored energy of said timing capacitor means comprises an adjustable current source connected to said timing capacitor means for effecting a flow of current through the latter, and means for adjusting said adjustable current source in dependence upon the position of said throttle valve.
 41. A system as defined in claim 32, wherein said means for adjusting said adjustable constantcurrent source in dependence upon at least one variable engine operating condition comprises fuel-enrichment means operative for so adjusting said adjustable constant-current source as to cause enrichment of the fuel-air combustion mixture during engine start-up.
 42. A system as defined in claim 41, wherein said adjustable constant-current source has an adjustment signal input for receipt of an adjustment signal, and wherein said fuel enrichment means comprises a Miller integrator circuit comprised of at least one amplifying transistor having a base, an emitter and a collector, a Miller integrating capacitor connected between the collector of said amplifying transistor and the base thereof, a collector resistor connected in the collector circuit of said amplifying transistor of said Miller integrator circuit, means comprised of a resistor and a diode connected between said adjustment signal input and the terminal of said Miller integrating capacitor which is connected to said collector of said amplifying transistor, and a transistor circuit stage comprised of a further transistor having a collector connected to the base of said amplifying transistor and having a base, and means connecting said base of said further transistor to the engine start switch.
 43. A system as defined in claim 41, wherein said adjustable constant-current source has an adjustment signal input for receipt of an adjustment signal, and wherein said fuel enrichment means comprises a Miller integrator circuit comprised of a first current supply line and a second current supply line, first and second amplifying transistors interconnected with and cooperating with each other, a Miller integrating capacitor having one terminal connected to the base of said first amplifying transistor and having another terminal connected to the collector of said second amplifying transistor, the emitter of said second amplifying transistor being connected to said first current supply line, means comprised of a diode and a resistor connecting the collector of said second amplifying transistor to said adjustment signal input, a collector resistor connecting the collector of said second amplifying transistor to said second current supply line, a resistor connecting the base of said first amplifying transistor to said first current supply line, a resistor connecting the emitter of said first amplifying transistor to said first current supply line, the emitter of said first amplifying transistor being connected to the base of said second amplifying transistor, and a transistor circuit stage comprised of a further transistor comprising a collector, a resistor connecting the collector of said further transistor to the base of said first transistor, the emitter of said first transistor being connected to said second current supply line, and means connecting the base of said further transistor to the engine start switch.
 44. A system as defined in claim 32, wherein said means for adjusting said adjustable constantcurrent source in dependence upon at least one variable engine operating condition comprises temperature compensation means operative for so adjusting said adjustable constant-current source as to vary the fuel-air combustion mixture in dependence upon engine temperature.
 45. A system as defined in claim 44, wherein said adjustable constant-current source has an adjustment signal input for receipt of an adjustment signal, and wherein said temperature compensation means comprises a voltage divider circuit Having a voltage-divider tap and comprised of a voltage-divider branch including a temperature-responsive component arranged in heat-exchanging relationship with the engine, and an emitter-follower transistor circuit stage including an emitter-follower transistor having a base connected to said voltage-divider tap, and means comprised of a resistor and a diode connecting the emitter of said transistor to said adjustment signal input.
 46. A system as defined in claim 45, wherein said temperature-responsive component is a negative-temperature-coefficient resistor.
 47. A system as defined in claim 1, wherein said triggering means comprises pulse-shaping means for imparting to said triggering pulses a well-defined shape, and wherein said pulse-shaping comprises a monostable multivibrator circuit comprised of first and second current supply lines connected to the terminals of a voltage source, a normally non-conductive first multivibrator transistor and a normally conductive second multivibrator transistor, a timing capacitor connected between the base of said second transistor and the collector of said first transistor, the collector-emitter paths of said first and second transistors being both connected across said first and second current supply lines, a charging transistor having a collector-emitter current path connected in series with said timing capacitor, a resistor connected in parallel with the base-emitter current path of said charging transistor, the base of said charging transistor being connected to the collector of said first transistor and the collector of said charging transistor being connected to the same one of said current supply lines as is connected the collector of said second transistor.
 48. A system as defined in claim 47, wherein said multivibrator circuit further includes a resistor having one terminal connected to the junction of the emitter of said charging transistor and said timing capacitor and having an other terminal connected to the same one of said current supply lines as is connected the emitter of said first transistor.
 49. A system as defined in claim 1, wherein said airflow sensing means comprises an airflow sensing member located in the air-intake passage and displaceable by the air flowing into the air-intake passage, and a potentiometer having a wiper mechanically connected to said displaceable airflow sensing member, and wherein the relationship between the voltage at the potentiometer wiper and the position of the potentiometer wiper is a predetermined non-linear relationship.
 50. A system as defined in claim 49, wherein said relationship is an exponential relationship.
 51. A system as defined in claim 49, wherein said airflow sensing means further includes a load resistor connected between said wiper and one end of said potentiometer and operative for establishing the desired non-linear relationship.
 52. In an internal-combustion engine, in combination, at least one engine cylinder, an air-intake passage communicating with the interior of said cylinder, a piston movable in such cylinder, an engine crankshaft connected to said piston, an ignition arrangement for igniting fuel-air mixture in said cylinder and including electromechanical ignition-signal generating means coupled to the engine crankshaft and operative for generating a train of electrical crankshaft-position-synchronized ignition signals, an electrically actuatable fuel-injection valve having an electrical input for receipt of a valve-opening pulse and operative for injecting fuel into said cylinder for a time interval corresponding to the duration of such valve-opening pulse, and a fuel-injection control system comprising airflow sensing means for determingin the rate of airflow through said air-intake passage of the engine, triggering means including electronic frequency divider means having an input connected to said ignition-signal generating means and operative for receiving said train of electrical ignition signals and converting the same into a lower-frequency train of electrical fuel-injection triggering pulses, and means connected to said triggering means for receipt of said triggering pulses and operative for generating a valve-opening pulse having a duration dependent upon the airflow rate detected by said airflow sensing means in response to generation of a fuelinjection triggering pulse.
 53. In an internal-combustion engine having at least one engine cylinder, an air-intake passage communicating with the interior of such cylinder, a piston movable in such cylinder, an engine crankshaft connected to such piston, an ignition arrangement for igniting fuel-air mixture in such cylinder and including electromechanical ignition-signal generating means coupled to the engine crankshaft and operative for generating a train of electrical crankshaft-position-synchronized ignition signals, and an electrically actuatable fuel-injection valve having an electrical input for receipt of a valve-opening pulse and operative for injecting fuel into such cylinder for a time interval corresponding to the duration of such valve-opening pulse, for use therewith, a fuel-injection control system comprising airflow sensing means for determining the rate of airflow through the air-intake passage of the engine; triggering means including electronic frequency divider means for receiving the train of electrical ignition signals and converting the same into a lower-frequency train of electrical fuel-injection triggering pulses; and means connected to said triggering means for receipt of said triggering pulses and operative for generating a valve-opening pulse having a duration dependent upon the airflow rate detected by said airflow sensing means in response to generation of a fuel-injection triggering pulse. 